An organic light emitting device includes generally two electrodes and an organic layer that is inserted into the electrodes. The organic light emitting device converts a current into visible rays by injecting electrons and holes from two electrodes into the organic layer. In order to improve performance, the organic light emitting device may further include an electron/hole injection layer or electron/hole transport layer as well as the organic layer that converts the current into the visible rays.
However, the interface between the electrode that is formed of metal, metal oxides or conductive polymers and the organic layer is unstable. Therefore, heat that is applied from the outside, internal occurrence heat, or an electric field that is applied to devices may negatively affect the performance of the device. In addition, because of a conductive energy level difference between the electron/hole injection layer or the electron/hole transport layer and the other organic layer that is adjacent thereto, a driving voltage for operating devices may be increased. Accordingly, it is important to stabilize the interface between the electron/hole injection layer or the electron/hole transport layer and the other organic layer as well as minimize an energy barrier for injecting electron/hole from the electrode to the organic layer.
The organic light emitting device has been developed so as to control the energy level difference between two or more electrodes and the organic layer that is positioned between the electrodes. In the organic light emitting device, the anode is controlled to have a Fermi energy level that is similar to HOMO (highest occupied molecular orbital) energy level of the hole injection layer, or a material that has the HOMO energy level that is similar to the Fermi energy level of the anode for the hole injection layer is selected. However, since it is required that the hole injection layer is selected in consideration of the Fermi energy level of the anode as well as the HOMO energy level of the hole transport layer or the light emitting layer that is adjacent to the hole injection layer, there is a limit in selecting a material for a hole injection layer. Therefore, while the organic light emitting device is manufactured, in general, a method for controlling the Fermi energy of the anode is adopted. However, a material for anode is limited.
Meanwhile, it is known that a performance characteristic of a device that has a multilayered organic layer is largely affected by a transportation ability of a charge carrier of the organic layer of each layer. While it is operated, a resistor loss occurring in the charge transport layer relates to conductivity, and the conductivity largely affects a required operation voltage as well as a heat load of a device. In accordance with the concentration of the charge carrier of the organic layer, a band bending phenomenon occurs at a point that is close to the contact point between the organic layer and the metal. By this phenomenon, injection of the charge carrier becomes easy, thereby reducing contact resistance.